PURPOSE: The goal of this in vivo study is to determine the feasibility and efficacy of suicide gene therapy using adenovirus-mediated herpes simplex virus thymidine kinase (HSV-TK) and the prodrug acyclovir (ACV) system in animal model of human prostate cancer.
MATERIALS AND METHODS: We used a replication-defective adenoviral vector containing the beta-galactosidase gene (Ad-CMV-beta-gal) as a control and Adenovirus-Cytomegalovirus-Thymidine Kinase (Ad-CMV-TK) as the therapeutic vector under the trascriptional control of the CMV promoter. Transduction efficiency was assessed in vitro by infection of LNCaP and PC-3 human prostate cancer cells with Ad-CMV-beta-gal utilizing X-gal staining. TK activity in LNCaP and PC-3 cells infected with Ad-CMV-TK was determined by measuring the TK-mediated [3H]-Ganciclovir (GCV) phosphorylation. Sensitivity of LNCaP and PC-3 cells to Ad-CMV-TK in vitro was determined after infection of therapeutic vector with or without ACV. Subcutaneous tumors were established in athymic nude(nu/nu) mice with PC-3 cells, and Ad-CMV-TK/ACV sucide gene therapeutic system-induced inhibition of tumor growth in vivo was determined in separate and controlled experiments.
RESULTS: The mean TK activity was significantly higher in Ad-CMV-TK-infected LNCaP and PC-3 cells than in cells infected with Ad-CMV-beta-gal that was used as a control(P<0.05). The growth of human prostate cancer cells with Ad-CMV-TK was significantly inhibited by the addition of GCV in vitro(p<0.05). In vivo experiments using PC-3 human prostate cancer animal model demonstrated that tumor volume and growth at the conclusion of experiment was significantly attenuated in the suicide toxic gene therapy (Ad-CMV-TK / ACV) group compared with Ad-CMV-TK, ACV and no treatment control groups(p<0.05).
CONCLUSIONS: Adenovirus-mediated suicide gene therapy using HSV-TK / ACV system provides an effective therapy in an experimental human prostate cancer animal model by significantly inhibiting tumor growth.